The present invention relates to sheet-perforating apparatus.
In order to manufacture perforated sheet material, as required for many different purposes, it is necessary to provide an apparatus capable of punching through the sheet material as the latter travels in order to achieve a continuously operating construction which will provide certain economies in the manufacture of the perforated sheet material. At the present time apparatus designed for this purpose suffers from several drawbacks. The known apparatus is extremely noisy and operates with a considerable amount of undesirable vibrations. The output which can be obtained with conventional apparatus is relatively low and continuous operation cannot be maintained over long periods of time because maintenance is required at frequent intervals. The maintenance operations of the conventional apparatus require special tools and special power supplies are sometimes required for the conventional apparatus.
In the case where the sheet material which is to be perforated is extruded, one of the problems encountered with conventional apparatus is that the speed with which the extruded sheet material can be punched, which is to say the linear speed of travel of the sheet material during the punching thereof, is of necessity less than the linear speed of the sheet material issuing from the extruder, so that a continuous operation from the extruder through the perforating apparatus cannot be achieved.
In addition, the material which is punched from the perforated sheet material accumulates undesirably and must be removed from time to time, creating undesirable labor costs.
One of the particular problems encountered is in connection with the formation of the perforations themselves. The punches tend to tear the sheet material instead of cutting cleanly therethrough. In order to solve this latter problem some punches take the form of hollow tubes having sharp cutting ends which operate in the manner of a cookie cutter cutting into the sheet material while pressing the latter against an anvil surface, but such constructions are not suitable for cutting through plastics or metals of the type required for venting soffits used in building structures. It has also been proposed to provide rotary anvils formed with bores which register with the punches and which receive the punches as they pierce through the sheet material so that in this way also an attempt has been made to provide cleanly cut perforations, but this construction also creates great problems in connection with proper registry of the bores of the anvil with additional problems being encountered in connection with removal of the punched material from the bores.